This invention relates generally to the use of transponders for position determining systems that make use of vehicle-mounted antennas and transponder devices. More particularly, this invention relates to a method and system for testing the integrity of a vehicle-mounted antenna in a position determining system.
Typically in order to identify the location of a vehicle, transponders are installed on the vehicle path at various locations. Coded information is stored in the transponders by means of tuned resonators. The coded information may include fixed data about distances from fixed reference points and may also include variable data relating, for example, to travel orders. Antennas which utilize a given frequency band and which emit an electromagnetic wave in that frequency band are positioned on the vehicle. When a vehicle transporting an antenna passes in the vicinity of a transponder and the antenna emits electromagnetic waves in a frequency band to which the transponder is tuned, the antenna""s electromagnetic waves power the transponder. This causes the resonator circuit in the transponder to resonate and results in the transmission of the data stored therein. This information is received by the antenna and transmitted to signal processing equipment coupled to the antenna for processing.
In the absence of transponders on the vehicle""s path, the antenna does not receive any transponder data transmissions. Therefore, a system making use of the antenna to receive transponder data would not find unusual the absence of transponder transmissions. When a defective antenna, which was previously located in non-transponder territory, enters transponder territory, the defective antenna fails to receive any transponder transmission. The failure to receive a transponder transmission may be problematic in particular if the position determining system makes use of these transmissions to coordinate vehicle traffic.
A deficiency of systems of the type described above is that they provide no practical way of determining whether the absence of transponder transmission is due to the absence of transponders or to a defective vehicle antenna.
Consequently there exists a need in the industry to provide an improved method, device and system for testing an antenna on a vehicle that alleviates at least in part the deficiencies of prior art methods and devices.
In accordance with a broad aspect, the invention provides a method for testing a vehicle antenna. A testing transponder responsive to an electromagnetic field of a vehicle antenna is provided. While positioned in the electromagnetic field of the vehicle antenna, the testing transponder is adapted to intermittently transmit signals conveying data in a format suitable to be detected by the vehicle antenna. The signals detected by the antenna are monitored to detect an error condition associated with the vehicle antenna. In a non-limiting example of implementation, an error condition associated with a vehicle antenna is detected when a time period since the last signal detected by the antenna exceeds a certain threshold time period.
Advantageously, in the absence of transponders on the vehicle path, the antenna continues to receive data transmissions from the testing transponder. Therefore, the absence of transponder transmissions, for a period of time exceeding a threshold, indicates a failure in the antenna. The receipt of transponder transmissions by the antenna confirms that the antenna is functioning namely that it is able to receive transponder transmissions.
Advantageously, providing a testing transponder adapted to emit intermittently rather than continuously reduces transmission conflicts between the testing transponder and a transponder on the vehicle path that is being powered by the antenna. The time between testing transponder transmissions is a trade-off between providing a long time delay to reduce the processing time required to monitor the transponder transmission and providing a time delay that is sufficiently short to provide the proper level of confidence that the antenna is functioning.
In a non-limiting implementation, the testing transponder is adapted to transmit a signal periodically such that the duration of the time periods between the transmissions is the same. Alternatively, the testing transponder may be adapted to transmit a signal non-periodically such that the duration of the time periods between the transmissions is different from one time period to the next.
In accordance with a broad aspect, the invention provides an apparatus for testing a vehicle antenna. The apparatus being responsive to an electromagnetic field of a vehicle antenna for intermittently transmitting signals conveying data in a format suitable to be detected by the vehicle antenna.
In accordance with another broad aspect, the invention provides a system including in combination a testing transponder and a monitoring unit. The testing transponder is responsive to the electromagnetic field of an antenna to intermittently transmit signals conveying data in a format suitable to be detected by the vehicle antenna. A monitoring unit monitors the signals detected by the antenna and detects an error condition associated with the vehicle antenna when the time since the last signal detected by the antenna exceeds a certain threshold time period.
In accordance with a specific implementation, the apparatus for testing a vehicle antenna includes a receiver, a processing unit and a transmitter. The receiver is responsive to the electromagnetic field of a vehicle antenna for generating a first power signal. The processing unit processes the first power signal to generate an intermittent power signal, where the intermittent power signal includes power segments. The transmitter is responsive to the power segments in the intermittent power signal to generate a succession of signals, each signal conveying data to be transmitted to the vehicle antenna.
In accordance with another broad aspect, the invention provides an apparatus for testing a vehicle antenna. The apparatus includes means responsive to an electromagnetic field of a vehicle antenna for generating a first power signal. The apparatus also includes means for processing the first power signal to generate an intermittent power signal, the intermittent power signal including power segments. The apparatus also includes means responsive to the power segments in said intermittent power signal for generating a succession of signals, each signal conveying data to be transmitted to the vehicle antenna.
Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.